a. Field of the Invention
The present invention relates to cardiac navigation technology. More specifically, the present invention relates to a cardiac navigation system including an electrode array for use therewith.
b. Background Art
Cardiac navigation systems are available to provide a means for a physician to locate a site within the heart of a patient for purposes of performing procedures such as tissue ablation. One type of cardiac navigation system includes a cardiac mapping catheter, and a series of active point electrodes disposed on the patient's skin along three approximately orthogonal axes. The cardiac mapping catheter is inserted into a heart chamber of the patient. The active electrodes are then activated to impose an electrical field across the three axes. Such electrical field is then detected by sensing electrodes on the cardiac mapping catheter. The sensing electrodes are then able to take electrophysiological and geometrical measurements, which are used to create an internal map of the heart chamber. Exemplary cardiac navigation systems are disclosed in U.S. Pat. Nos. 5,553,611, 5,662,108, 5,697,377, 5,983,126, 6,728,562, 6,939,309, 6,947,785, and 6,990,370, the disclosures of which are hereby incorporated in their entirety herein, by reference thereto.
One problem with current cardiac navigation systems, however, is their three-dimensional accuracy. For example, although the determination of the location of the catheter is relatively reliable for the purpose of marking a specific site, and thus facilitating return to that site, such systems do not always provide a sufficiently accurate three-dimensional surface model of the heart chamber. Specifically, “location distortion,” caused by inherent limitations in cardiac navigation systems, results in surface model distortions.
Moreover, comparison between the resulting surface model and high resolution images of the heart chamber, such as those obtained from Ultrasound, CT or MRI scans, do not match. Location distortion is the result of two primary factors: 1) irregular conductivity of the body tissue; and 2) inconsistencies in current driven across the three approximately orthogonal axes.
The ideal cardiac navigation system would drive a uniform current through a conductive volume of uniform conductivity across each axis. However, the human body does not present a uniform conductivity. A person's blood, heart tissue, lungs, muscle, etc., all have different conductivity. Secondly, current navigation systems fail to create a uniform sheet of current across each axis. Instead, relatively small electrodes are used to drive currents across each axis. In addition, it is known from the construction of such electrodes that more current emanates from the center of the electrode, where the wires that carry the current fan-out, than from the edges and corners.